Radio receiving system



July .31, 1934. R. BRUNI l RADIO RECEIVING SYSTEM Filed Jfine 11, 1929 R- Bram Patented July 31, 1934 UNITED STATES PA'TENTi OFFICE 1,968,739 name RECEIVING SYSTEM.

Riccardo Bruni, I Genoa, Italy Application June 11, 1929, and No. 370,070-

In Italy June 23, 1928 ,3 1 Claim. (01. 250-20) This invention relates to, a selective wireless telephonic system devised to be free of the inconveniences occasioned by interfering currents due to atmospheric conditions, .such interfering currents often having a frequency substantially equal to that of the currents employed for transmission. In the selective wireless telephonic system according to the present invention the signals are impressed in known manner on an intermediate frequency current modulating the carrier'wave. By way of example, the intermediate frequency may be'20,000 cycles; At the receiving station the intermediate frequency is selected, after passing through a receiver, by a coil and a condenser in series and, tuned to the intermediate frequency. Interfering currents are neutralized by a shielded inductance. to the intermediate frequency by a parallel condenser, is coupled to the first coil and also to a heterodyne oscillator to produce beats which are received in a telephone. Shields protect the devices following the receiver from external dis-' turbances.

The accompanying drawing shows, by way of example, and diagrammatically, an embodiment of the invention.

Fig. 1 shows diagramatically the arrangement of the transmitter station and Fig. 2 the arrange- ,ment of the receiving station. Fig. 3 is a diagram of a modification of the receiving station.

Referring to the drawing, 1 denotes the transmitter set for generating a carrier wave, for example, of 300 meters, and 2 and 3 denote the connections between the transmitter set and the microphone circuit 4. In the connection 3 is included a coil 5 inductively coupled to the coil 6 of the heterodyne generator 7. The current generated in the coil by the generator 7 of an intermediate frequency, for instance, 10,000 meters, is superposed on the microphonic current passing through the connections 2 and 3. For simple wireless telephonic transmission the coil 5 is connected directly to the transmitter apparatus 1.

8 denotes an ordinary receiver provided with an antenna 21 and ground connection 23 and of which the terminals are connected to the circuit including the coil 9 and a series connected condenser 10 tuned to the intermediate frequency.

A coil 11 tuned to the intermediate frequency by the parallel condenser 12 is inductively coupled to both the coil 9 and to the coil 14 of a heterodyne oscillator 15.

Interfering currents are neutralized by the inductance 16 having the shield 17.

A second coil, tuned- I'he tuned coils 9'and'11 are provided with a shield 18 represented by dotted lines in Fig. 2.

13 denotes the telephone connected with the circuitof the coil 11.

The'theory according to which the reception apparatus ofisets the separation of the desired signals from parasitic currents is that, while there is detectedlthe wave carrying the interm diate current on which is impressed the signal, in' the case of the parasitic current there is detected a low frequency current. It is of course easy to separate the signals at high frequency from low frequency currentscorresponding to disturbances.

Two stages of rectification are used.

The local heterodyne generates a current of such frequency that, when superposed on the in termediate frequency current received from the transmission station, there is obtained a beat current, whereasit is not possible to produce beats with the low frequency parasitic currents detected. i

- The receiving apparatus according to the form of invention illustrated in Fig. 3 incorporates a detector valve and a neutralizer valve, so arranged that the current variations provided by the detector valve are opposed to the current variations provided by the neutralizer valve in such manner as completely to neutralize the high fre-- quency or intermediate frequency parasitic currents.

While currents of low frequency as well as of high frequency and intermediate frequency pass through the detector valve I permit the passage of high frequency or intermediate frequency currents only through the neutralizer valve. With this object the primary coil 9, Fig. 2, in the embodiment illustrated in Fig. 3 is connected at its middle point to the positive pole of the anode battery through a condenser in such manner that one half of said primary coil 9 is traversed by the high frequency or intermediary frequency parasitic current from the detector valve, while the other half of said coil is traversed by the equal and opposed high frequency or intermediate frequency current which traverses the neutralizer valve.

Referring in detail to Fig. 3, 21 denotes the aerial antenna, 22 the inductancefor the regulation of the valve, and 23 the earth, all included in the receiving apparatus indicated generally at 8. 24 denotes the detector valve and 25 denotes the neutralizer valve. 26 denotes a condenser and 27 denotes a resistance connected to the negative pole of the filament battery 31. 28 denotes the anode battery.

The aerial picks up the waves and applies them, by means of the lead 35, to the grids 24 and 25' of the valves 24 and 25; 28 denotes the anode battery, 31 the filament battery, 26 the grid condenser and 27 the grid resistance; the provision of the condenser 26 and resistance 27 only on the circuit of the valve 24 causes the incoming wave to be detected in the circuit that is inserted between the terminals 29'-29"; in other words, valve 24 acts as detector. Further, the valve 25 works only as amplifying valve and therefore, at the terminals 29-29 the incoming wave is amplified. The aerial 21 picks up the transmitted wave as well as the waves disturbing the reception.

The disturbing waves, as usual, by reason of the detection effected within valve 24, set up in the circuit that is inserted between 29'-29", disturbing low-frequency currents while the incoming wave causes, in the said circuit inserted between the terminals 29--29", a detected current possessing the relatively high frequency of the wave generated by the device 7 of the transmitting station, Figure 1 and modulated by the low-frequency current to be transmitted, generated by the device 4 (microphone, microphonicamplifier or the like) of the transmitting station.

On the contrary, the terminals 29-29, the disturbing waves and the transmitted wave (modulated by the other wave of the microphone signal) being simply amplified, there result high frequency currents.

The circuits respectively connected to 29-29 and 29'-29" are equal. They work as follows: the current generated by the device 7 (Fig. 1) flows through the circuit 29"-30 9'--1030'- 29 being prevented from flowing through the circuit, including 16. The disturbing currents detected being at low-frequency, the flow through the circuit 16 cannot pass through the circuit 9 and therefore, the separation of the current set, up by the disturbances is attained. But, as the rent which is equal (through adjustment of the valves and in the circuit connected with.

detecting valve 24, besides producing the said low frequency disturbing currents, permits also the passage of disturbing current at high frequency (1. e. it works partially also as an amplifier as well as detector), it follows that said high frequency disturbing currents, also pass the winding 9 thus influencing the reception. To annul such effect, there is provided the valve 25 which sets up in the winding 9" a high frequency disturbing cura suitable usual circuits) to the high frequency disturbing current flowing through the circuit 9. As the fluxes of the windings 9' 9" are in opposition and act in opposi- 'tion in the winding (11) the latter will not be influenced by the effect of the disturbances.

The windings 16 are connected in series with the source of anode current supply 28 and the anodes of valves 24 and 25.

The coil 14 of a heterodyne oscillator 15 is inductively coupled to the coils 9 and 9" and generates a current of such frequency that, when superposed on the intermediate frequency current received from the transmission station, there is obtained a beat current, whereas it is not possible to produce beats with the low frequency parasitic currents detected.

What I claim is:

In a receiver for a carrier wave which is modulated by'the current resulting from the modulation of a high frequency wave, sufficiently different from the frequency of the carrier wave, by means of the microphonic current, a detecting device, a high frequency amplifier device, parallel input circuits coupling the detecting andamplifier device to an antenna, the outputs of said devices being connected symmetrically with a balanced coil arrangement, and a high frequency heterodyne oscillator and a reproducer coupled to the balanced coil arrangement.

RICCARDOv BRUNI.

device 

